Search results for "Interactions"

Tropical Temperate Toughs over southern Africa: mechanisms and evolution in response to climate change

2015

In the Southern Hemisphere, Southern Africa and the south-west Indian Ocean are one of the three preferred regions where interactions between the tropics and midlatitudes develop. This is the South Indian Convergence Zone (SICZ), where northwest-southeast oriented cloud bands form at the synoptic scale (between 3 and 5 days). These bands are mainly found during the austral summer and are commonly referred to as tropical temperate troughs (TTTs). This research aims at improving our knowledge related to TTTs, with a study on the dynamics associated with these systems, and an analysis of their possible evolution during the 21st century.The first part of this thesis aims at identifying favorab…

Achieving Strong Positive Cooperativity through Activating Weak Non-Covalent Interactions

2018

Positive cooperativity achieved through activating weak non-covalent interactions is common in biological assemblies but is rarely observed in synthetic complexes. Two new molecular tubes have been synthesized and the syn isomer binds DABCO-based organic cations with high orientational selectivity. Surprisingly, the ternary complex with two hosts and one guest shows a high cooperativity factor (α=580), which is the highest reported for synthetic systems without involving ion-pairing interactions. The X-ray single-crystal structure revealed that the strong positive cooperativity likely originates from eight C-H⋅⋅⋅O hydrogen bonds between the two head-to-head-arranged syn tube molecules. Thes…

Strategies for Exploring Functions from Dynamic Combinatorial Libraries

2020

Two Polymorphic Forms of a Six-Coordinate Mononuclear Cobalt(II) Complex with Easy-Plane Anisotropy: Structural Features, Theoretical Calculations, a…

2016

A mononuclear cobalt(II) complex [Co(3,5-dnb)2(py)2(H2O)2] {3,5-Hdnb = 3,5-dinitrobenzoic acid; py = pyridine} was isolated in two polymorphs, in space groups C2/c (1) and P21/c (2). Single-crystal X-ray diffraction analyses reveal that 1 and 2 are not isostructural in spite of having equal formulas and ligand connectivity. In both structures, the Co(II) centers adopt octahedral {CoN2O4} geometries filled by pairs of mutually trans terminal 3,5-dnb, py, and water ligands. However, the structures of 1 and 2 disclose distinct packing patterns driven by strong intermolecular O-H···O hydrogen bonds, leading to their 0D→2D (1) or 0D→1D (2) extension. The resulting two-dimensional layers and one-…

Chalcogen‐Bonding Interactions in Telluroether Heterocycles [Te(CH2)m]n(n=1–4;m=3–7)

2020

The Te⋅⋅⋅Te secondary bonding interactions (SBIs) in solid cyclic telluroethers were explored by preparing and structurally characterizing a series of [Te(CH2 )m ]n (n=1-4; m=3-7) species. The SBIs in 1,7-Te2 (CH2 )10 , 1,8-Te2 (CH2 )12 , 1,5,9-Te3 (CH2 )9 , 1,8,15-Te3 (CH2 )18 , 1,7,13,19-Te4 (CH2 )20 , 1,8,15,22-Te4 (CH2 )24 and 1,9,17,25-Te4 (CH2 )28 lead to tubular packing of the molecules, as has been observed previously for related thio- and selenoether rings. The nature of the intermolecular interactions was explored by solid-state PBE0-D3/pob-TZVP calculations involving periodic boundary conditions. The molecular packing in 1,7,13,19-Te4 (CH2 )20 , 1,8,15,22-Te4 (CH2 )24 and 1,9,17,…

Bringing a Molecular Plus One: Synergistic Binding Creates Guest-Mediated Three-Component Complexes

2020

Cethyl-2-methylresorcinarene (A), pyridine (B), and a set of 10 carboxylic acids (Cn) associate to form A·B·Cn ternary assemblies with 1:1:1 stoichiometry, representing a useful class of ternary systems where the guest mediates complex formation between the host and a third component. Although individually weak in solution, the combined strength of the multiple noncovalent interactions organizes the complexes even in a highly hydrogen-bond competing methanol solution, as explored by both experimental and computational methods. The interactions between A·B and Cn are dependent on the pKa values of carboxylic acids. The weak interactions between A and C further reinforce the interactions betw…

2,4,5-Trimethylimidazolium Scaffold for Anion Recognition Receptors Acting Through Charge-Assisted Aliphatic and Aromatic C–H Interactions

2016

A series of two-armed 2,4,5-trimethylimidazolium-based oxoanion receptors, which incorporate two end-capped photoactive anthracene rings, being the central core an aromatic or heteroaromatic ring, has been designed. In the presence of HP2O7(3-), H2PO4(-), and SO4(2-) anions, (1)H- and (31)P NMR spectroscopical data clearly indicate the simultaneous occurrence of several charge-assisted aliphatic and aromatic C-H noncovalent interactions, i.e., significant downfield shifts were observed for the imidazolium C(2)-CH3 protons, the methylene N-CH2 protons, and the inner aromatic proton or the outer heteroaromatic protons. Density functional theory calculations confirm the occurrence of these non…

Adsorption of triblock copolymers and their homopolymers at laponite clay/solution interface. Role played by the copolymer nature

2009

The adsorption thermodynamics of copolymers, based on ethylene oxide (EO) and propylene oxide ( PO) units, at the laponite (RD) clay/liquid interface was determined at 298 K. The copolymer nature was tuned at molecular level by changing the hydrophilicity, the architecture and the molecular weight (Mw) keeping constant the EO/PO ratio. Polyethylene (PEGs) and polypropylene (PPGs) glycols with varying Mw and their mixture were also investigated to discriminate the role of the EO and the PO segments in the adsorption process. Enthalpies of transfer of RD, at fixed concentration, from water to the aqueous macromolecule solutions as functions of the macromolecule molality were determined. They …

Biophysical approaches for the study of metal-protein interactions

2019

Protein-protein interactions play important roles for a variety of cell functions, often involving metal ions; in fact, metal-ion binding mediates and regulates the activity of a wide range of biomolecules. Enlightening all of the specific features of metal-protein and metal-mediated protein-protein interactions can be a very challenging task; a detailed knowledge of the thermodynamic and spectroscopic parameters and the structural changes of the protein is normally required. For this purpose, many experimental techniques are employed, embracing all fields of Analytical and Bioinorganic Chemistry. In addition, the use of peptide models, reproducing the primary sequence of the metal-binding …

Synthesis, characterization, and complexation of tetraarylborates with aromatic cations and their use in chemical sensors.

2005

Five aromatic borate anions, namely tetrakis(4-phenoxyphenyl)borate (1), tetrakis(biphenyl)borate (2), tetrakis(2-naphthyl)borate (3), tetrakis(4-phenylphenol)borate (4), and tetrakis(4-phenoxy)borate (5), have been prepared and tested as ion-recognition sites in chemical sensors for certain aromatic cations and metal ions. To gain further insight into the complexation of the cations, some complexes have been prepared and structurally characterized. The complexation behavior of 1 and 2 towards N-methylpyridinium (6), 1-ethyl-4-(methoxycarbonyl)pyridinium (7), tropylium (8), imidazolium (9), and 1-methylimidazolium (10) cations has been studied, and the stability constants of the complexes o…